Ionia, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.6 °C (low) to 18.4 °C (high). Annual precipitation averages 1104.9 Millimeters. Ionia is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.9 °C | 4.1 °C | 46.74 mm |
| February | -4.8 °C | 6.8 °C | 53.59 mm |
| March | 0.4 °C | 12.8 °C | 74.42 mm |
| April | 5.9 °C | 18.7 °C | 117.86 mm |
| May | 11.9 °C | 23.4 °C | 130.81 mm |
| June | 17.1 °C | 28.4 °C | 133.35 mm |
| July | 19.4 °C | 30.9 °C | 109.73 mm |
| August | 18.3 °C | 30.4 °C | 101.85 mm |
| September | 13.8 °C | 26.4 °C | 114.81 mm |
| October | 7 °C | 19.9 °C | 90.42 mm |
| November | 0.9 °C | 12.7 °C | 76.2 mm |
| December | -4.4 °C | 6.3 °C | 55.12 mm |
| Annual | 6.6 °C | 18.4 °C | 1104.9 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |